1. Field of the Invention
The present invention relates to an ink jet printer and particularly to such an ink jet printer in which ink is supplied from an ink tank via a flexible tube (i.e., a flexible ink supply tube) to a recording head mounted on a movable carriage. The present invention also relates to such an ink jet printer which can collect air bubbles produced in an ink flow channel and discharge the air bubbles.
2. Discussion of Related Art
Patent Document 1 (Japanese Patent Application Publication No. 63-17056 A) or Patent Document 2 (Japanese Patent Application Publication No. 7-121583 B2) discloses a tube-supply-type ink jet printer in which ink is supplied from an ink tank provided in a housing, via a flexible tube, to a recording head mounted on a carriage movable in the housing.
More specifically described, in the ink jet printer disclosed by Patent Document 1, the recording head has a plurality of ink ejection nozzles vertically arranged in an array, a plurality of ink supply channels communicating with the ink ejection nozzles, respectively, and a common ink chamber (i.e., a damping chamber) communicating with each of the ink supply channels. The ink supply channels and the common ink chamber are formed in the recording head, such that the common ink chamber opens in one vertical side surface of the head. The ink is supplied from the ink tank provided in the housing, via the flexible tube, to the common ink chamber of the recording head. A portion of the side surface of the recording head in which the common ink chamber opens is liquid-tightly closed by a flexible membrane (i.e., a pressure-change damping membrane). An ink flow inlet opens in the bottom race of the common ink chamber (the damping chamber) and is opposed to the flexible membrane.
A plurality of actuators in the form of piezoelectric elements are fixed to another potion of the side surface of the recording head, such that the actuators are aligned with the ink supply channels, respectively. When an arbitrary one of the actuators is driven or operated, a pressure is applied to the ink present in a corresponding one of the ink supply channels, so that a droplet of ink is ejected from a corresponding one of the ink ejection nozzles toward a recording sheet.
In the ink jet printer disclosed by Patent Document 2, the recording head has a plurality of ink ejection nozzles vertically arranged in an array, a plurality of ink supply channels vertically arranged in an array, and a plurality of piezoelectric elements fixed to two opposite, vertical side surfaces of the head. When an electric voltage is applied to an arbitrary one of the piezoelectric elements, the one piezoelectric element is deformed, so that a droplet of ink is ejected from a corresponding one of the ink ejection nozzles via a corresponding one of the ink supply channels. The ink is supplied from the ink tank provided in the housing, via the flexible tube, to a damper case (i.e., a damping chamber) which is mounted on the carriage and which supplies the ink to each of the ink supply channels of the recording head The damper case includes a first member having an opening in one vertical side surface thereof, a second member having respective openings in two opposite, vertical side surfaces thereof and a filter sheet sandwiched by the open side surface of the first member and one of the two open side surfaces of the second member. The other open side surface of the second member is liquid-tightly closed by a flexible membrane. The first member has, in a lower end portion thereof an ink flow inlet communicating with the flexible tube connected at one end thereof to the stationary ink tank, and the second member has, in a lower end portion thereof an ink flow outlet communicating with each of the ink supply channels of the recording head.
In each of the ink jet printers disclosed by Patent Documents 1, 2, when the carriage is reciprocated, in particular, when the carriage is returned, inertia is exerted to the ink flowing in the flexible tube connecting between the stationary ink tank and the movable carriage, and accordingly the pressure of the ink supplied to,the recording head (or each of the ink ejection nozzles) is largely changed. This change of pressure of the ink is damped or absorbed by the deformation of the flexible membrane of the damping chamber, so that respective droplets of ink can be ejected from the respective nozzles with respective uniform ejection pressures and a recording quality of the recording head can be maintained.
However, in each of the ink jet printers disclosed by Patent Documents 1, 2, the damping chamber is vertical and one vertical side surface of the damping chamber is liquid-tightly closed by the flexible membrane. Thus, in the case where the ink jet printer employs a plurality of recording heads for the purpose of ejecting a plurality of sorts of color inks, respectively, and respective damper cases of the recording heads that define respective damping chambers corresponding to the color inks are arranged such that the damper cases are arranged parallel to each other it is required that the damper cases he appropriately spaced from each other so as to allow the flexible membrane of each damper case to deform by an appropriate amount. However, this leads to increasing the size of the apparatus mounted on the carriage and the total number of components of the apparatus, thereby increasing the production cost of the ink jet printer.
In addition, in the ink jet printer disclosed by Patent Document 2, a plane on which the ink flow inlet opens in the damping chamber is perpendicular to a plane on which the filter sheet or the flexible membrane extends, that is, a direction in which the ink flows from the ink flow inlet is parallel to the plane on which the filter sheet or the flexible membrane extends. In addition, the ink flow inlet opens at a position remote from the flexible membrane. Thus, the ink flowing at increased speeds out of the ink flow inlet does not directly act on the flexible membrane. More specifically described, first, the pressure increase of the ink, caused by inertia, directly acts on the flexible filter sheet, and the filter sheet is largely flexed because it cannot instantaneously allow all the increased amount of the ink to pass therethrough. Consequently the pressure of the ink present on the downstream side of the filter sheet is quickly increased, and then the flexible membrane is elastically deformed to increase the volume of the downstream-side chamber and thereby lower the increased pressure of the ink. Thus, the ink present in each ink ejection nozzle may be largely influenced by the pressure change of the ink caused by the inertia
Also, in the ink jet printer disclosed by Patent Document 1, a great distance is present between a plane on which the ink flow inlet opens in the damper chamber and a plane on which the flexible membrane extends. Thus, the pressure increase of the ink, caused by inertia, does not directly act on the flexible membrane, and accordingly the flexible membrane cannot efficiently damp or absorb the pressure change of the ink.
In the above-indicated tube-supply-type ink jet printer, if air bubbles (i.e., air) are contained in the ink present in the recording head, the recording head may fail to eject the ink, or otherwise the recording quality of the head may lower. In this type of ink jet printer, however, air cannot be avoided from permeating the flexible tube and dissolving in the ink, because of the natural property of the material used to form the tube. Thus, it has been needed to provide an air-bubble collecting chamber on an upstream side of the recording head, collect or accumulate the air bubbles in the collecting chamber, and remove the thus collected air bubbles.
Hence, in a tube-supply-type ink jet printer disclosed by Patent Document 3 (Japanese Patent Application Publication No. 2000-103084 A), a recording head has, in an upper portion thereof an ink manifold (i.e., an air-bubble collecting chamber), and an ink tank and a circulating pump are fixed in position in a housing. The circulating pump is driven or operated to circulate the ink from the ink tank to a first ink flow passage, then the manifold, a second ink flow passage, and again the ink tank, so that the air bubbles produced in the circulation channel are returned to the ink tank and are removed. Meanwhile, at a waiting position in the housing, a sucking and purging device sucks ink from an ink ejection nozzle of the recording head.
However, in the above-indicated ink jet printer, it is needed to employ an ink returning tube for circulating the ink from the circulating pump back to the ink tank. Thus, the ink jet printer is complicated and is increased in size.
Furthermore, Patent Document 4 (Japanese Patent Application Publication No. 2002-240310 A) discloses an ink jet printer in which air produced in the form of air bubbles in an ink supply tube is accumulated in an upper portion of a tank mounted on a carriage, is discharged through a communication port by an air discharging pump, and then the communication port is air-tightly closed by an air discharging valve. However, the construction of the air discharging valve is not described in detail.
When the air discharging pump does not suck the air from the air-bubble collecting chamber, for example, when the recording head records images (e.g., letters and/or symbols) on a recording medium, the air discharging valve needs to air-tightly close the communication port and thereby stably keep the ink and the air bubbles in the air-bubble collecting chamber. On the other hand, when the recording head is checked for its maintenance, the air discharging valve needs to quickly open the communication port so as to communicate with an outside space and thereby discharge the air bubbles from the air-bubble collecting chamber.
In addition, since the air discharging valve is mounted on the carriage, the valve is repeatedly reciprocated with the carriage, during the recording operation of the ink jet printer. Therefore, the air discharging valve needs to have a small size, a light weight, and a simple construction.